1. Field of the Invention
The present invention relates to a method of manufacturing a porous metal foam, and more particularly to a method of manufacturing a porous metal foam containing pores having a nano size.
2. Description of the Prior Art
A porous metal foam is a porous metal containing numerous regular pores in a metal material, and is classified into an open cell (OC) type and a closed cell (CC) type. In the closed cell type metal foam, pores in a metal are not connected but present independently, and in the open cell type metal foam, those in the material are connected to each other such that a gas or fluid can pass through. Thus, the open cell type metal foam can provide a high density of surface area and can be used in functional applications requiring such need.
The open cell metal foam morphologically corresponds to a duodechahedronal structure similar to that of a human bone which is a structurally perfect stable isotropic structure, and has a wide surface area which cannot be mechanically realized, in addition to the structural stability.
Currently, the fields to which the open cell type metal foam is widely applied in advanced countries are aircraft industry requiring high efficiency, small size and light weight, vehicles, power plants, heat exchangers of power devices, heat radiating plates of semiconductor devices, silencers for large-scale plants, catalysts of chemical factories, aircrafts requiring high strength and ultra light weight, structural materials of space industry, fuel cells, and filters, and are gradually being expanded until now. Due to the global trends, a demand on the open cell type metal foam is increasing also in Korea.
A technology according to the related art includes a method of forming a nickel or copper layer on a surface of a polyurethane foam through physical vapor deposition and growing a nickel or copper layer through electrolytic plating to manufacture a metal foam having a nanoscale open porous structure in which nanopores are connected to each other, but the method requires a complex process such as physical vapor deposition and it is difficult to manufacture a thick porous foam as deposition rates of the surface and interior of the foam are different when the pores are fine.
Further, since a heat-resistant temperature of the polyurethane foam used as a frame is low and polyurethane is evaporated in an in-use environment of high temperature, fine pores are left in the final metal product at a site where polyurethane used to be as the polyurethane is generally evaporated during the production process and structural strength is lowered.
In order to overcome the disadvantages, there has been an attempt to form a nickel plating layer on a surface of carbon foam, but this technology has just demonstrated on a microporous-scale level, but not on nano-scale.